Stable Phase Diagram of Quaternary Water–Salt System Li+, Na+, Cs+//SO42––H2O at T = 298.2 K

The stable phase diagram of quaternary water–salt system Li+, Na+, Cs+//SO42––H2O was studied at T = 298.2 K by the isothermal dissolution equilibrium method. The solubility and physicochemical properties (density and refractive index) of the equilibrium solution were measured. Moreover, the composition of the solid phase was identified using the X-ray diffraction method. There are seven solids formed in this system at research temperature, including four single salts and three double salts, which are lithium sulfate monohydrate (Li2SO4·H2O), sodium sulfate (Na2SO4), sodium sulfate decahydrate (Na2SO4·10H2O), cesium sulfate (Cs2SO4), and double salts Li2SO4·Cs2SO4, 3Li2SO4·Cs2SO4·2H2O, and 3Na2SO4·Li2SO4·12H2O, respectively. Thus, the stable phase diagram of the quaternary water–salt system contains 5 invariant points, 11 univariant curves, and 7 crystallization regions. The size order of the salts’ crystalline phase region is Li2SO4·Cs2SO4 > 3Na2SO4·Li2SO4·12H2O > 3Li2SO4·Cs2SO4·2H2O > Na2SO4·10H2O > Li2...